1. Field of the Invention
The present invention generally relates to a frequency-scan traveling wave antenna, and more particularly to a frequency-scan traveling wave antenna which operates at frequencies in the millimeter wave range.
2. Description of the Prior Art
Frequency-scan traveling wave antennas are known in the art. Typically, uses of such antennas include their use in collision avoidance radar and in imaging radar. However, such frequency-scan traveling wave antennas are burdened by disadvantages, and those disadvantages adversely affect the quality of their performance. This interferes with the use of such antennas as an effective component of collision avoidance radar systems and imaging radar systems.
Problems with traveling wave antennas of the prior art include the following: inferior radiating element design, inadequate impedance match, insufficient power weighting accuracy, and inferior phase coherence across an array.
Accordingly, there is a need for the development of a frequency-scan traveling wave antenna which enables frequency scanning of an antenna beam at millimeter wave frequencies, where the beam and the side lobe levels are at an improved degree of controllability and performance over those of the antennas of the prior art. Moreover, there is a need for the development of a frequency-scan traveling wave antenna having an optimized radiating element design, improved impedance match, improved power weighting accuracy, and better phase coherence across the array, thereby enabling accurate design of beam width and side lobe level.
The present invention generally relates to a frequency-scan traveling wave antenna, and more particularly, to a frequency-scan traveling wave antenna which operates at millimeter wave frequencies. In particular, the present invention provides a high performance traveling wave antenna which scans by frequency, and which can be used effectively as a component of collision avoidance radar systems and imaging radar systems.
The frequency-scan traveling wave antenna of the present invention uses an impedance matching transformer at the input of each radiator element to compensate for radiated power in the element, and allows the input impedance of the radiator element to be the same as its output impedance. This is in contrast to conventional traveling wave radiators, which do not use impedance matching to correct for impedance shifts arising from radiated energy. The specific use of impedance matching at each element in the traveling wave frequency scan antenna of the present invention reduces reflections, and provides better control over array design.
The present invention also provides an arrangement of radiators and delay lines which are geometrically symmetric, thereby balancing stray radiation and minimizing the amount of degradation of the beam pattern and the side lobe levels due to radiation from the delay lines between the radiator elements.
To summarize, the traveling wave antenna of the present invention uses impedance matched radiator elements and a symmetric layout. This enables the invention to achieve an accurate degree of control over power weighting at each radiator element, resulting in improved side lobe levels and a narrow beam at millimeter wave frequencies.
Therefore, it is a primary object of the present invention to provide a frequency-scan traveling wave antenna operating at millimeter wave frequencies.
It is an additional object of the present invention to provide a high performance antenna which scans by frequency, and which can be used effectively in collision avoidance radar systems and imaging radar systems.
It is an additional object of the present invention to provide a frequency-scan traveling wave antenna having an optimized radiating element design.
It is an additional object of the present invention to provide a frequency-scan traveling wave antenna having improved impedance match.
It is an additional object of the present invention to provide a frequency-scan traveling wave antenna having improved power weighting accuracy.
It is an additional object of the present invention to provide a frequency-scan traveling wave antenna providing better phase coherence across the array, thereby enabling accurate design of beam width and side lobe level.
It is an additional object of the present invention to provide a frequency-scan traveling wave antenna which employs an arrangement of radiators and delay lines which is geometrically symmetric, thereby balancing stray radiation and minimizing the amount of degradation of the beam pattern and the side lobe levels due to radiation from the delay lines between the radiators.
The above and other objects, and the nature of the invention, will be more clearly understood by reference to the following detailed description, the associated drawings, and the appended claims.